1. Technological Field
The present disclosure relates generally to the field of data networking and telecommunications. More particularly, in one exemplary aspect, the present disclosure is directed to the intelligent configuration of scrambling operation to accommodate e.g., both scrambling and non-scrambling connections (such as to e.g., legacy type devices).
2. Description of Related Technology
HDMI (High-Definition Multimedia Interface) (see, inter alia, www.hdmi.org) is an exemplary dominant digital audio/video interface technology specified by the HDMI Founders. Current incarnations of the standard specify support for simple networking of digital audio/visual (A/V) interconnects, intended to be used primarily between an arbitrary assembly of multimedia “sources” (e.g., set-top boxes, DVD players, Blu-ray Disc players, video game consoles, computers or CPUs) and “sinks” (e.g., display monitors, home-theater system, etc.). This interconnection is generally unidirectional in nature; i.e., from source to sink, in current implementations.
As a brief aside, the current revision of HDMI (HDMI 1.4) utilizes TMDS (Transition Minimized Differential Signaling) to transmit video, audio and auxiliary data over three main HDMI data lanes via one of three modes. FIG. 1 illustrates these TMDS modes in an exemplary 720×480p video frame. The three modes include: (1) a video data period in which the pixels of an active video line are transmitted; (2) a data island period in which audio and auxiliary data are transmitted; and (3) a control period which occurs between video and data island periods. HDMI utilizes TMDS in order to send 10-bit characters that are transmission minimized encoded.
During control periods, control symbols are transmitted repeatedly on the three HDMI main data lanes. HDMI defines four control symbols, representing the four values 0b00, 0b01, 0b10 and 0b11. The value transmitted on lane zero represents whether HSYNC, VSYNC, both or neither is/are being transmitted, and the values transmitted on lanes 1 and 2 are set to non-zero during preambles. Preambles are constructed from eight identical control symbols and are used to signify imminent transitions to data island periods or video data periods. Table 1 illustrates the preambles used for each data period type (i.e., TMDS mode).
TABLE 1CTL0CTL1CTL2CTL3Data Period Type1000Video Data Period1010Data Island PeriodAdditionally, Table 2 illustrates the control signal-assignment on each of the three main TMDS channels.
TABLE 2TMDSChannel(Lane)D0D10HSYNCVSYNC1CTL0CTL12CTL2CTL3The two control signals used for each of the TMDS channels are encoded into ten-bit codes as follows:
case (D1, D0):   0, 0: q_out [9:0] = 0b1101010100;   0, 1: q_out [9:0] = 0b0010101011;   1, 0: q_out [9:0] = 0b0101010100;   1, 1: q_out [9:0] = 0b1010101011;endcase;
As can be seen from above, these ten-bit codes used for the four control symbols have predominant clock pattern content (i.e., a significant amount of transmissions of 0101 bit-pattern sequences). Furthermore, the control symbols for control values 0b10 and 0b11 are not DC balanced, which results in a significant baseline “wander” during the time that VSYNC is transmitted. Note also that VSYNC is often used in negative parity, which means that the VSYNC value transmitted is “0” when VSYNC is asserted, and “1” when VSYNC is not asserted (depending on the video frame specific resolution details).
HDMI uses the unique high-transition content of these control symbols to distinguish them from other types of symbols used in HDMI. The high-transition content can be detected by the receiver, and the control symbols may be used by the receiver to perform symbol alignment when first acquiring the incoming signal stream (so-called symbol alignment synchronization).
Unfortunately, existing HDMI implementations may produce undesirable electromagnetic interference (EMI) with nearby wireless services (for example: Wi-Fi, PAN (e.g., Bluetooth), and/or cellular services). The resultant radio frequency interference can negatively impact, for example, an end user's Wi-Fi bandwidth, and reduce cellular bandwidth (or drop cellphone calls) when the appropriate wireless services are used simultaneously with HDMI. Such a problem is exacerbated in devices in which HDMI is used in close proximity with other wireless services, such as in a laptop computer, a tablet, or a smart phone.
Various solutions for handling the electromagnetic emissions have been proposed. For example, in incipient HDMI proposals, the use of scrambling for control symbols is mandatory for certain transmission speeds (e.g., above 340 million Tcharacter/sec/channel, where a Tcharacter comprises 10 bits of information that represent a byte of data or a control symbol according to the TMDS encoding specification). It is currently anticipated that scrambling may be required for all transmission rates. Those of ordinary skill in the related arts will readily appreciate that where a scrambler is used to transmit a data stream, a descrambler must be used within the receiver to descramble the received data stream. Consequently, in order to support both future and legacy products, the Assignee hereof ideally desires methods and apparatus configured to intelligently enable and/or disable scrambling capabilities.
Improved apparatus and methods are needed to configure scrambling and non-scrambling compatibilities, such as when designing for a broad spectrum of possible usage scenarios. More specifically, such apparatus and methods would, inter alia, provide for mechanisms that intelligently negotiate/determine scrambling and/or non-scrambling operation when connected to a peer device.